The invention relates to a coupling device between an elongate control bar, with longitudinal movement, intended for a nuclear reactor and a mechanism for driving the bar. It finds a particularly important, although not exclusive, application in light water cooled moderated reactors, using control bars comprising a cluster of parallel elements, containing a neutron absorbing material, which elements have a great length and so considerable flexibility and are suspended, at their upper end, from a piece generally called "spider".
Control bar coupling devices are already known of the type comprising a gripper body having resilient gripping fingers, belonging to the mechanism and, on the bar, a terminal pommel for engagement by the fingers and a shoulder directed towards the pommel. The coupling device comprises an additional member, such as a sleeve, movable with respect to the gripper body between a position in which it allows resilient fingers to be released from the pommel and another position in which it locks the resilient fingers onto the pommel.
In all these known coupling devices, the bar is simply suspended from the drive mechanism. Because of the very slender shape of the elements, because of their construction (generally a stack of pellets in a thin sheath), because of the disymmetrie and of the diversity of means for guiding them, considerable vibrations may appear during operation of the reactor. The coupling device cannot absorb the forces having a torque with respect to an axis passing through the gripping zone. The resilient blades work under poor conditions since, because of their very shape, they are only adapted for withstanding tractive forces. The inevitable clearances risk causing oscilltions and vibrations in the vertical direction.